DESCRIPTION: (Applicant's abstract) Changes in extracellular space (ECS) have been studied within the context of a variety of neuropathologies, particularly those associated with head injury. Somewhat surprisingly, ECS has been relatively neglected within the epilepsy field, even though there are several studies that suggest contributions of ephaptic interactions (i.e., current flow through extracellular space) to increased excitability, hyper-synchrony, and seizure spread. Further, experiments have shown that changes in extracellular osmolality can modify brain seizure threshold. Finally, recent studies from the applicant's laboratory have shown that a commonly used diuretic, furosemide, is "anticonvulsant" in tests against a number of in vitro and in vivo models. The applicant proposes to examine potential mechanisms by which modulation of ECS may affect tissue excitability and epileptogenicity. The applicant will: 1) test a number of agents that modulate ECS in intact animal models of seizure and status epilepticus; 2) measure neuronal and glial swelling, and related changes in ECS, during epileptiform activity in hippocampal slices; 3) treat "epileptic" slices with agents that alter ECS, and correlate drug effects of ECS (and cell swelling) with their anti-epileptic actions; and 4) study changes in cell properties (voltage-dependent currents, changes in intracellular calcium) when tissue is exposed to agents that cause cell swelling. These studies will constitute an initial integrated attempt to examine the relationship of cell swelling (and changes in ECS) to epileptiform activity. Such an approach may open unexplored avenues for the development of new anti-epileptic agents -- approaches that may be especially useful in dealing with medically-intractable seizures as well as in prophylactic treatment of "at risk" head injury patients.